Books: NRA Illustrated Firearms Assembly Handbook
You find the neatest things in used bookstores, like the "Illustrated Firearms Assembly Handbook," a collection of articles that originally appeared in NRA publications in the 1950s. Each article examines the design and history of a particular firearm, often giving a parts breakdown or field-stripping instructions.
As you might imagine, many of the guns in the book have been out of production for years. There are plenty that have soldiered on, though (there's a whole section on M1911 disassembly). Some firearms have also been reintroduced in various forms, like the Supermatic Trophy:
The Safety Hammerless.
The Walther P38.
There are neat little sections on famous gun designers and gun-related court cases (this was about the time the NRA shifted its focus to politics).
Overall, it's a cool book, and the parts diagrams it contains might be very useful if you own one of the classic firearms featured.